Distributed control systems (DCS) are used in a variety of process industries including chemical, petrochemical, refining, pharmaceutical, food and beverage, power, cement, water and wastewater, oil and gas, pulp and paper, and steel, and are used to control batch, fed-batch, and continuous processes operating at a single site or at remote locations. Process plants typically include one or more process controllers communicatively coupled to one or more field devices via analog, digital or combined analog/digital buses, or via a wireless communication link or network. Collectively, the various devices perform monitoring, control, and data collection functions to control the process, safety shutdown systems, fire and gas detection systems, machine health monitoring systems, maintenance systems, decision support, and other systems.
The field devices, which may be, for example, valves, valve positioners, switches and transmitters (e.g., temperature, pressure, level and flow rate sensors), are located within the process environment and generally perform physical or process control functions such as opening or closing valves, measuring process parameters, etc. to control one or more process executing within the process plant or system. Smart field devices, such as the field devices conforming to the well-known Fieldbus protocol may also perform control calculations, alarming functions, and other control functions commonly implemented within the controller. The process controllers, which are also typically located within the plant environment, receive signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices and execute a controller application that runs, for example, different control modules which make process control decisions, generate control signals based on the received information and coordinate with the control modules or blocks being performed in the field devices, such as HART®, WirelessHART®, and FOUNDATION® Fieldbus field devices. The control modules in the controller send the control signals over the communication lines or links to the field devices to thereby control the operation of at least a portion of the process plant or system.
Information from the field devices and the controller is usually made available over a data highway to one or more other hardware devices, such as operator workstations, personal computers or computing devices, data historians, report generators, centralized databases, or other centralized administrative computing devices that are typically placed in control rooms or other locations away from the harsher plant environment. Each of these hardware devices typically is centralized across the process plant or across a portion of the process plant. These hardware devices run applications that may, for example, enable an operator to perform functions with respect to controlling a process and/or operating the process plant, such as changing settings of the process control routine, modifying the operation of the control modules within the controllers or the field devices, viewing the current state of the process, viewing alarms generated by field devices and controllers, simulating the operation of the process for the purpose of training personnel or testing the process control software, keeping and updating a configuration database, etc. The data highway utilized by the hardware devices, controllers and field devices may include a wired communication path, a wireless communication path, or a combination of wired and wireless communication paths.
As an example, the DeltaV™ control system, sold by Emerson Process Management, includes multiple applications stored within and executed by different devices located at diverse places within a process plant. A configuration application, which resides in one or more workstations or computing devices, enables users to create or change process control modules and download these process control modules via a data highway to dedicated distributed controllers. Typically, these control modules are made up of communicatively interconnected function blocks, which are objects in an object oriented programming protocol that perform functions within the control scheme based on inputs thereto and that provide outputs to other function blocks within the control scheme. The configuration application may also allow a configuration engineer to create or change operator interfaces which are used by a viewing application to display data to an operator and to enable the operator to change settings, such as set points, within the process control routines. Each dedicated controller and, in some cases, one or more field devices, stores and executes a respective controller application that runs the control modules assigned and downloaded thereto to implement actual process control functionality. The viewing applications, which may be executed on one or more operator workstations (or on one or more remote computing devices in communicative connection with the operator workstations and the data highway), receive data from the controller application via the data highway and display this data to process control system designers, operators, or users using the user interfaces, and may provide any of a number of different views, such as an operator's view, an engineer's view, a technician's view, etc. A data historian application is typically stored in and executed by a data historian device that collects and stores some or all of the data provided across the data highway while a configuration database application may run in a still further computer attached to the data highway to store the current process control routine configuration and data associated therewith. Alternatively, the configuration database may be located in the same workstation as the configuration application.
In many distributed process control systems, each field device in the process plant is assigned a unique device tag. The unique device tag provides an easy way to reference the corresponding field device. Device tags may be used during the configuration of the process control system to specify the source or destination, respectively, of an input or output to a function block in a control module. Each signal type has associated with it a particular format or set of information, and the device tag for a particular device may have associated with it a specific signal type such that when the device tag is associated with an input or output of a function block, the function block knows the format and information associated with the signal. In cases in which a field device has multiple signals associated with it (e.g., a valve may measure and transmit both pressure and temperature), device signal tags may be associated with each signal of the field device.
For a variety of reasons, access to data of the process control system has traditionally been available only while on the process plant premises and/or while using a device connected to the data highway that couples the operator workstations, controllers, data historians, and other equipment. Security is a particular concern with respect to process control systems and, as such, process control system operators generally physically separate the process control system from external network environments (e.g., the internet) to limit or prevent opportunities for outside actors to cause damage to the process control system, affect product quality or viability, or access or steal proprietary information.
More recently, a few mobile solutions have emerged that allow users to view some information from the process control system via mobile devices such as smart phones, even when not coupled directly to the process networks and data highways that make up the process plant. These solutions allow monitoring of a single data source such as a data historian, and so the available data are limited to those data that are stored in the data historian (i.e., a small subset of the total data in the process plant). Additionally, even the data that are available via such systems are not available in real-time (because of the frequency with which data are stored to the data historian). Further, due to the delays in data availability, and the limited subset of data available, alarms are generally not available via the mobile systems presently offered and, to the extent alarm-like functionality may be available on some mobile systems, the alarms are either not “native” to the process control system (i.e., they are provided as a layer on top of the mobile system and require extensive and time-consuming engineering to implement) or lack the real-time and historical data necessary to evaluate and troubleshoot the alarms.